GM gives birth to a new generation of V-6 powerplants that promise to be world class.

Once the preserve of luxury car powerplants, variable valve timing is now spreading to more mainstream engines. Case in point: the arrival of General Motors’ new ‘high feature’ global V-6 engine family, the first engine from GM to feature VVT on both intake and exhaust camshafts.

The first of this V-6 family, a 3.6L will make its debut in Cadillac’s 2004 CTS, replacing its existing, U.K.-sourced 3.2L V-6. The new 255 hp CTS motor is one of several versions of the modular V-6, which will also come in 2.8L and 3.2L displacements, to be used in major markets worldwide. Engine size can be expanded to 3.8L, or as large as 4.0L when the cylinder liners are eliminated in favor of bore coatings.

Versions of the engine will be both naturally aspirated and turbocharged and applications will include front-, rear- and all-wheeldrive, as well as hybrid vehicles.

One key to the new engine family’s success, maintains GM, is that it will be competitive with the best in the V-6 class, such as the Honda/Acura 3.2L and Toyota/Lexus 3.0L units, yet be built at a lower cost. All GM’s V-6s will share the following features: aluminum construction, dual overhead camshafts, fourvalve- per-cylinder valvetrain, roller-finger followers, continuously variable cam phasing, electronic throttle control, forged-steel crankshaft, piston-cooling oil jets, coolant-loss protection software, GM’s oil-life system, 32 bit microprocessor and coil-on-plug ignition.

A valve in the dualstage manifold closes to boost cylinder charging in the low- to midspeed range. It opens at higher speeds to feed all cylinders from a common larger plenum.

GM says the output of the most powerful variant of the new engine family will exceed 370 hp, with torque in excess of 350 lbs.-ft.

Work on the new V-6 family started in 1999, and was completed in record time, says Tim Cyrus global V-6 chief engineer.

“The goals for the engine were industry leading reliability, flexibility, package size, pleasibility, efficiency and value,” Cyrus says. The engine can be easily integrated into most platforms, has industry leading NVH and performance with three discrete combustion systems MPFI, SIDI and turbo.”

Importantly, the V-6 engine architecture was designed to incorporate different options, in order to create a broad range of configurations. As well as normally aspirated/ sequential port fuel injection ‘foundation’ architecture, there are two potential major variants. One is a spark-ignition direct-injection (SIDI) V-6 of either 2.8L or 3.2L displacement. To account for differing market regulations and conditions, particularly in Europe, the engine design can accommodate both stratified-charge (lean-burn) and stoichiometric- charge SIDI architectures. Also in the pipeline are turbocharged 2.8L or 3.2L variants, with a variety of power and torque outputs depending on specific content.

As well as its adaptability, the key feature of GM’s V-6 family is its use of variable valve timing. Moving to full VVT eliminates the traditional compromise in engine design between power and torque outputs, and also improves fuel economy and lowers emissions. In the case of the 3.6L engine, the improvement in torque output is notable: 90 percent of the 252 lbs-ft. peak torque is available across a broad operating range, from 1,600 to 5,800 rpm.

Compared to an existing GM double overhead cam V-6, the 3.6L develops 20 percent more peak power, a 13 percent increase in peak torque — and a 24 percent increase in torque-integral, or the amount of torque available at most points throughout the rpm range.

“Flexibility was very important,” says Bob Jacques, base engine design system engineer. “We insisted on going after high performance and high refinement at the same time.”

A 32-bit micro-hybrid engine control unit embeds all of the necessary electronic circuitry on a four layer substrate that reduces the size of the unit. The new design can be engine mounted, freeing up valuable engine compartment space.
The four-cam continuously variable cam phasing system is electronically controlled and hydraulically actuated. The phasers allow intake cam adjustment through 50 degrees of crankshaft rotation and 50 degrees for exhaust-cam adjustment.

An added benefit of the VVT system is that it allowed for the elimination of the exhaust gas recirculation system, thus reducing weight and complexity.

The V-6’s intake system includes a dualstage variable manifold. A valve in the manifold changes the plenum volume available for resonance tuning of the inlet flow path. When the valve is shut, the cylinders feed from two separate plenums. In this mode the system boosts cylinder charging in the low- to midspeed range. At higher engine speeds, the valve opens and the cylinders all feed from a common larger plenum.

Another significant technical advance is the V-6’s 32-bit micro-hybrid engine control unit, which GM claims is the most powerful currently used in the industry. The ECU design embeds all of the necessary electronic circuitry on a four-layer ‘sandwich’ substrate that reduces the size of the control unit. More robust and resistant to vibration than previous ECUs, the new design can be engine mounted. This move frees valuable space in the engine bay and eliminates attachment problems at the assembly plant.

The four-cam continuously variable cam phasing system is electronically controlled and hydraulically actuated. The phasers allow intake cam adjustment through 50 degrees of crankshaft rotation and 50 degrees for exhaust-cam adjustment.
One function of the ECU is torque-based engine control strategy. Engine output for the driver’s desired throttle opening is determined by the ECU. The torque-based strategy calculates optimal throttle position, variable intake manifold position, continuously variable cam phasing positions and various other operational inputs and then translates that information into an ideal throttle position. GM says the torque-based engine control strategy is superior to early electronically controlled throttle-based engine-management systems that relied only on the throttle position sensor to govern throttle opening.

In terms of detail refinements, Jacques says the target was to be class leading. “We went after all the benchmarks,” he says. “You name it — if there is a good V-6 out there, we found out how and why it was good.”

Refinement measures include specially isolated cam covers, which incorporate an isolated gasket around the cover perimeter and radial lip seals at the tubes through which each spark plug is inserted. These components decouple the cam cover from vibration created by the combustion process.

The structural aluminum oil pan is attached by a full-circle mounting that enhances bending stiffness. Specially contrived curves on the major panel surfaces and the sidewalls mitigate ‘drumming’ from the oil pan.

The engine front cover has internal damping plates that quell vibrations caused by the engine. The steel plates, made in two different thicknesses ‘tune’ at differing frequency from the aluminum front cover; the frequency separation dampens noise output.

While several rival Japanese V-6 engines use belt cam drives, GM Powertrain chose chain drives for the new engine family. “We went with chains for longer life,” says Jacques. “The Japanese engines have used belts because they are less expensive and quieter, but they are also moving to chains now.” In the case of GM’s new V-6, Jacques says the noise of the camshaft drive chain engaging the sprocket teeth is reduced by use of molded-rubber ‘cushion rings’ on the crankshaft sprocket.

GM plans to assemble its new V-6 engine family for all global applications at plants in St. Catharines, Ontario, Canada and Port Melbourne, Victoria, Australia.

Beyond the Cadillac CTS, initial North American market applications for the 3.6L V- 6 include Cadillac’s forthcoming mid-sized Rendezvous.

I noticed that premium fuel is recommended. However, the CTS owners manual states 87 octane fuel is recommended, and that premium can be used but is not required. Are there any known consequences with the 87 octane?

Aurora5000

03-15-05, 08:55 AM

You don't have quite as much power but the 20 cent difference in price per gallon made it a good tradeoff for me.

Thanks,
Steve

PS, when we were looking at other brands of cars comperable to the CTS, all of the other V6's REQUIRED premium fuel.

ktills45

05-04-05, 09:31 PM

Ok, what does coolant loss protection software mean, exactly? :hmm:

wick05

05-05-05, 08:02 PM

Ok, what does coolant loss protection software mean, exactly? :hmm:

it helps the engine eleminate cylinders if all of the coolant is drained from the engine. That way the engine does not build up as much heat and you can use the oil for cooling. I think the range is about 20 miles. No quotes on that.

ktills45

05-06-05, 07:00 AM

it helps the engine eleminate cylinders if all of the coolant is drained from the engine. That way the engine does not build up as much heat and you can use the oil for cooling. I think the range is about 20 miles. No quotes on that.

Is it essentially the same type of system the N* uses? Because that would be pretty nice to have on board.

Aurora5000

05-13-05, 12:50 PM

The loss of coolant "limp home" mode is automatically initiated by the PCM if it senses extraordinarily high coolant temps based on input from the coolant sensor in the cylinder head.

The coolant temp sensor location was developed such that it senses coolant temp circulating thru the head when it is "wet" or covered by coolant. Should the coolant level fall even slightly in the engine the sensor will be uncovered as it is near the highest point in the head coolant jacket. If uncovered, or "dry", the sensor is designed and positioned such that it will sense the rapidly rising temperature of the exhaust port wall, thus responding to high "high metal temps" as well.

Before this happens the low coolant warning should be on and two different coolant temp warnings should be displayed.

When the PCM senses that the temp sensor is so hot that it has to be 'dry" and uncovered it switches in to the "limp home" mode to keep the engine running without damage so that you can drive to a safe place.

The limp home system works by turning the fuel injectors off to cylinders allowing them to stop running but they still pump air thru the cylinders to cool them down. Those cylinders will be shut down for a predetermined number of cylinder firing events while the others provide power. After the predetermined interval those cylinders start firing as the injectors are reactivated and the other cylinders are turned off by disabling the injectors so that they can cool. The two groups of cylinders shut down in sequence. The cylinder group operation is regulated not by a timer but actually by counting the number of firing events each group sees. This was much more effective at protecting the engine than a simple timer. In limp home mode you will notice that the two groups switch much more slowly at idle and then rapidly at higher speeds because of this.

There are other things done with the idle speed, fueling, spark advance, etc. in concert with the cylinder cut out but the main function that makes the limp home system work is the cylinder cut out. Remember, the valves are still operating so the cylinder still pumps air thru it...making it an internally air cooled engine when in limp home mode. This is often confused with the DOD (displacement on demand) system upcoming on GM engines and the older V-8-6-4 system on the 81 Cadillacs. They are not the same as the Northstar limp home mode.

If the engine needs to implement the limp home mode it can safely go 50 miles at 50 MPH with no damage. This has been tested and documented by several biased testers and ended up proving that it DOES work very well)

If limp home mode is ever used the engine oil should be changed immediately after when the cooling problem is being fixed. The oil gets extremely hot when the engine reverts to limp home mode as the oil takes over part of the task of cooling the engine.

:dance:

ktills45

05-16-05, 09:12 PM

Thanks for the infol. :thumbsup:

Aurora5000

05-31-05, 12:08 PM

Thanks

2004CTS

02-16-06, 08:49 AM

You don't have quite as much power but the 20 cent difference in price per gallon made it a good tradeoff for me.

Thanks,
Steve

PS, when we were looking at other brands of cars comperable to the CTS, all of the other V6's REQUIRED premium fuel.
Yes, this is what I found in my research as well. Many people don't realize how quickly the incremental cost of gas can be when you drive a lot.